Tethered cord syndrome is a rare intraspinal anomaly, Pediatric tethered cord syndrome: response of scoliosis to untethering procedures

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1 J Neurosurg Pediatrics 4: , 4: , 2009 Pediatric tethered cord syndrome: response of scoliosis to untethering procedures Clinical article Ma t t h e w J. McGi r t, M.D., 1 Vi v e k Me h ta, B.S., 1 Gi a n n i n a Ga r c e s-am b r o s s i, B.S., 1 Or e n Go t t f r i e d, M.D., 1 Ca n So l a k o g l u, M.D., 2 Zi ya L. Go k a s l a n, M.D., 1 Am e r Sa m d a n i, M.D., 3 a n d Ge o r g e I. Ja l l o, M.D. 1 1 Department of Neurosurgery, Johns Hopkins Hospital, Baltimore, Maryland; 2 Department of Orthopedics and Traumatology, GATA Haydarpasa Hospital, Istanbul, Turkey; and 3 Shriner s Pediatric Hospital, Philadelphia, Pennsylvania Object. Tethered cord syndrome (TCS) is frequently associated with scoliosis in the pediatric population. Following spinal cord untethering, many patients continue to experience progression of spinal deformity. However, the incidence rate, time course, and risk factors for scoliosis progression following tethered cord release remain unclear. The aim of this study was to determine factors associated with scoliosis progression and whether tethered cord release alone would halt curve progression in pediatric TCS. Methods. The authors retrospectively reviewed 27 consecutive pediatric cases of spinal cord untethering associated with scoliosis. The incidence rate and factors associated with scoliosis progression (> 10 increased Cobb angle) after untethering were evaluated using the Kaplan-Meier method. Results. The mean age of the patients was 8.9 years. All patients underwent cord untethering for lower-extremity weakness, back and leg pain, or bowel and bladder changes. Mean ± SD of the Cobb angle at presentation was 41 ± 16. The cause of the spinal cord tethering included previous myelomeningocele repair in 14 patients (52%), fatty filum in 5 (18.5%), lipomeningocele in 3 (11%), diastematomyelia in 2 (7.4%), arthrogryposis in 1 (3.7%), imperforate anus with an S-2 hemivertebra in 1 (3.7%), and lipomyelomeningocele with occult dysraphism in 1 (3.7%). Mean follow-up was 6 ± 2 years. Twelve patients (44%) experienced scoliosis progression occurring a median of 2.4 years postoperatively and 8 (30%) required subsequent fusion for progression. At the time of untethering, scoliosis < 40 was associated with a 32% incidence of progression, whereas scoliosis > 40 was associated with a 75% incidence of progression (p < 0.01). Patients with Risser Grades 0 2 were also more likely to experience scoliosis progression compared with Risser Grades 3 5 (p < 0.05). Whereas nearly all patients with Risser Grades 0 2 with curves > 40 showed scoliosis progression (83%), 54% of patients with Risser Grades 0 2 with curves < 40 progressed, and no patients with Risser Grades 3 5 with curves < 40 progressed following spinal cord untethering. Conclusions. In this experience with pediatric TCS-associated scoliosis, patients with Risser Grades 3 5 and Cobb angles < 40 did not experience curve progression after tethered cord release. Patients with Risser Grades 0 2 and Cobb angles > 40 were at greatest risk of curve progression after cord untethering. Pediatric patients with TCSassociated scoliosis should be monitored closely for curve progression using standing radiographs after spinal cord untethering, particularly those with curves > 40 or who have Risser Grades 0 2. (DOI: / PEDS08463) Ke y Wo r d s tethered cord syndrome scoliosis outcome progression stabilization Risser grade Tethered cord syndrome is a rare intraspinal anomaly, caused by abnormal spinal cord fixation and resultant low-lying and immobile conus medullaris. 20 The incidence of TCS is estimated to be 0.05 to 0.25 per 1000 births. 5,19 Tethered cord syndrome may result from Abbreviations used in this paper: AP = anteroposterior; TCS = tethered cord syndrome. many causes, including intraspinal lipoma, lipomyelomeningocele, diastematomyelia, spina bifida occulta, tight or thickened filum terminale, or scarring from previous myelomeningocele repair. 7 In addition to pain, neurological dysfunction, and urological dysfunction, pediatric TCS is frequently associated with scoliosis. 10 As many as 18% of patients presenting with congenital scoliosis have a contributory intraspinal abnormality. 9 More recent reports 270 J Neurosurg: Pediatrics / Volume 4 / September 2009

2 Response of scoliosis to untethering procedures have suggested that as many as 20 58% of cases of congenital scoliosis may be associated with intraspinal abnormalities. 1,2,10,12 14 Tethered cord as a direct cause of scoliosis was first demonstrated in 1990 by McLone et al. 8 after they observed stabilization or improvement in scoliosis in patients after myelomeningocele repair and tethered cord release. They postulated that scoliosis may develop as a consequence of ischemic cord injury at the site of tethering, subsequent dysfunction in sensory pathways, and associated asymmetrical paravertebral muscular tone. Winter et al. 21 and McMaster 9 originally demonstrated the safety and efficacy of primary correction of TCS with a subsequent planned scoliosis correction 3 6 months later. With increasing evidence for the safety of concurrent tethered cord release and spinal fusion, many authors are now performing a single-stage operation for concurrent TCS release and scoliosis correction. 3,16 However, as suggested by McLone and colleagues, growing evidence suggests that tethered cord release alone may lead to curve stabilization in some patients. 4,11,14,18 To date, the incidence rate, time course, and patient subgroups most likely to stabilize or progress after tethered cord release remain undefined. Therefore, we attempted to retrospectively analyze our experience in pediatric patients with TCS-associated scoliosis to determine the incidence rate, time course, and factors associated with progression of scoliosis following untethering. J Neurosurg: Pediatrics / Volume 4 / September 2009 TABLE 1: Risser sign scale Grade Radiological Sign 0 no evidence of ossification center over the iliac crest on the AP pelvis view 1 appearance of the ossification center over the lateral 0 25% 2 appearance of the ossification center over the lateral 25 50% 3 appearance of the ossification center over the lateral 50 75% 4 appearance of the ossification center over the lateral % but the ossification center is not completely fused to the iliac crest 5 complete fusion of the ossification center to the entire iliac crest Methods This study was approved by the Johns Hopkins Institutional Review Board committee. From our database of 115 consecutive pediatric patients who underwent spinal cord untethering between 1996 and 2006, we identified 27 patients who presented with TCS-associated scoliosis. The medical records for these patients were retrospectively reviewed and included all hospital records, all pre- and postoperative clinic notes, and all pre- and postoperative radiographs. Patient demographics, presenting symptoms, neurological deficits, extent of spinal deformity, and perioperative morbidity were assessed. Preoperative skeletal maturity was assessed from preoperative standing radiographs and classified at the time of surgical care using the Risser sign, 15 an indicator of skeletal maturity based on the amount of calcification present in the iliac apophysis (grade range 0 5; Table 1). Preoperative Cobb angles were recorded from 36-inch AP and lateral radiographs obtained within 4 weeks prior to tethered cord surgery. All reviewed patients underwent primary tethered cord release to address symptoms, including leg and back pain, or clinical signs of neurological dysfunction, without a planned postoperative scoliosis surgery. All patients with meningomyelocele underwent tethered-cord release for worsening pain and/or worsening urinary function. Urinary dysfunction was assessed by urology follow-up and urodynamics. Those patients classified as showing urinary improvement demonstrated both objective urodynamic evidence of improved bladder function as well as improved patient-assessed control. Routine follow-up consisted of clinical and radiographic assessment at 1, 3, 6, and 12 months after surgery, and again every 6 months postoperatively. Patients demonstrating curve progression often underwent more frequent clinical follow-up beyond 12 months postoperatively. Standard radiographic follow-up consisted of standing 36-inch AP and lateral scoliosis radiographs. All patients were monitored by both the neurosurgical and orthopedic departments. For the purposes of this study, postoperative scoliosis progression was defined as a > 10 increase in Cobb angle. 11 Only those patients with a Cobb angle > 10 were included in this series. Skeletally immature patients with scoliosis < 50 were first treated conservatively using bracing. Patients with sequential scoliotic curve progression (as demonstrated on 36-inch radiographs) underwent curve correction and instrumented fusion, despite tethered cord release and external bracing. Patients with stable spinal deformity underwent attempted curve correction and fusion only if their condition was accompanied by progressive radicular symptoms, worsening back pain, or progressively worsening functional limitations believed to arise from the spinal deformity. Time to deformity progression or fusion was defined as the time from tethered cord release. Statistical Analysis Progression-free survival and fusion-free survival were assessed using the Kaplan-Meier method. 6 Patients not experiencing progression or fusion were censored at the time of last follow-up. As determined a priori, curve progression and spinal fusion were assessed, stratified by skeletal maturity (Risser Grades 0 2 or 3 5) and Cobb angle (> 40 or < 40 ) via log-rank analysis (Statview, SAS Institute, Inc). Parametric data were expressed as means ± SDs and compared using the Student t-test. Nonparametric data were expressed as medians (interquartile range) and compared using the Mann-Whitney U-test. Percentages were compared using the Fisher exact test. Results Patient Population Of the 115 pediatric patients presenting with symptomatic TCS for first-time spinal cord untethering, 27 (23%) 271

3 M. J. McGirt et al. presented with associated scoliosis. All patients underwent tethered cord release for lower-extremity weakness, back and leg pain, or progressing bowel and bladder dysfunction. Patient demographics, symptomatology, and scoliosis measurements are given in Table 2. Sixteen patients were male (59%) and the mean age was 8.9 ± 3 years. The cause of tethering included previous myelomeningocele repair in 14 patients (52%), fatty filum in 5 (18.5%), lipomeningocele in 3 (11%), diastematomyelia in 2 (7.4%), arthrogryposis in 1 (3.7%), imperforate anus with S-2 hemivertebrae in 1 (3.7%), and lipomyelomeningocele with occult dysraphism in 1 (3.7%). Seventeen children (63%) were classified as Risser Grades 0 2 and 10 children (37%) as Risser Grades 3 5. There were 8 patients with Risser Grades 3 5 with curves < 40. The mean patient age at the last follow-up evaluation was 16.6 years (range years). Fourteen (52%), 12 (44%), and 15 (56%) patients presented with TCS symptoms of worsening motor paresis, pain, and urinary dysfunction, respectively (Table 2). Sixteen patients (59%) presented with a single structural curve and 11 (41%) presented with a double curve. The mean Cobb angle of the primary curve at the time of tethered cord release was 41 ± 16 (range ). Nineteen patients (70%) presented with a primary curve < 40 (mean 26 ± 9 ) and 8 (30%) presented with a primary curve > 40 (mean 50 ± 12 ). The primary curve apex was TABLE 2: Summary of patient demographics, symptomatology, and scoliosis measurements* Variable Value demographics mean age (yrs) 8.9 ± 3 male 16 (59) skeletal maturity at TCS Risser Grades (63) Risser Grades (37) cause of TCS postmyelomeningocele repair 14 (52) fatty filum 5 (18.5) lipomeningocele 3 (11) diastematomyelia 2 (7.4) arthrogryposis 1 (3.7) lipomyelomeningocele w/ occult dysraphism 1 (3.7) imperforate anus w/ S-2 hemivertebrae 1 (3.7) presentation lower-extremity paresis 14 (52) back & leg pain 12 (44) urinary dysfunction 15 (56) curve characteristics Cobb angle at TCS op 41 ± 16 thoracic apex 11 (41) thoracolumbar apex 10 (37) lumbar apex 6 (22) kyphosis 5 (18.5) * All values are number of patients (%), unless otherwise indicated. thoracic in 11 patients (41%), thoracolumbar in 10 (37%), and lumbar in 6 (22%). Five patients (18.5%) also presented with a kyphotic deformity (mean 43 ). Nine patients (33%) demonstrated spinal abnormalities that included 7 with hemivertebrae, 1 with butterfly vertebrae, and 1 with wedge vertebrae. The incidence of curve progression (44%) was not greater in this patient population with spinal abnormalities. Four patients (15%) demonstrated a TCS-associated syrinx, and the incidence of progression in this cohort was 50% compared with 47% in patients without an associated syrinx. Neurological Outcome All patients underwent lumbar tethered cord release. Ten (83%) of 12 patients reported significant improvement in back, lower-extremity, or perineal pain; 12 (86%) of 14 experienced improvement in lower-extremity motor dysfunction; and 12 (80%) of 15 experienced improvement in urinary dysfunction. Median time to resolution of pain, motor, and urinary dysfunction was 5.2, 4.8, and 5.7 months, respectively. Of 21 patients experiencing symptomatic improvement, 16 (76%) improved within 6 months of surgery. Of the 14 patients with a history of myelomeningocele repair, 64% experienced improvement of their TCS-associated declining motor deficits, 57% showed improvement in their preoperative pain, and 71% demonstrated improvement in their TCS-associated declining bladder function. Overall, 10 (37%) experienced retethering at a mean of 39.2 months after surgery, and all required revision untethering. For patients experiencing retethering, the incidence of deformity progression was 60%, similar to those not experiencing retethering (53%). Four (40%) of the 10 patients undergoing revision untethering experienced improvement of progressing motor deficits, five (50%) experienced improvement in preoperative pain, and 4 (40%) experienced improvement in TCS-associated declining bladder function. Progression of Spinal Deformity Mean follow-up duration was 6 ± 2 years. Seventeen patients (63%) postoperatively experienced > 5 Cobb angle improvement. Of these 17 patients, only 3 subsequently demonstrated curve progression. Four patients (15%) experienced > 15 Cobb angle improvement after tethered cord release. The incidence of progression in the patients with as opposed to those without myelomeningocele was 57% and 54%, respectively. Of the 14 patients with meningomyelocele, the vast majority (11 [79%]) were ambulatory. Two of the 3 nonambulatory patients progressed after undergoing untethering. Overall, 12 patients (44%) experienced scoliotic progression. In these patients, progression occurred a mean of 29 months after tethered cord release (Fig. 1). Eight (30%) required subsequent fusion for curve progression (Fig. 2); the mean extent of curve progression was 22 ± 6. A Cobb angle > 40 compared with an angle < 40 at the time of TCS surgery was associated with a 5.9-fold increase in the hazard of curve progression (hazard ratio = 5.945; p = ). For patients undergoing spinal cord untethering with curves < 40, only 6 (32%) progressed, at a mean of 54 months postoperatively. For patients under- 272 J Neurosurg: Pediatrics / Volume 4 / September 2009

4 Response of scoliosis to untethering procedures TABLE 3: Five-year incidence rate of radiological progression and subsequent fusion in 4 subgroups of patients with TCS-associated spinal deformity Cobb Angle/ Risser Grades No. of Patients % w/ Radiological Progression % w/ Subsequent Fusion <40 / <40 / >40 / >40 / Fig. 1. Graph of scoliosis progression-free survival in pediatric patients with TCS-associated scoliosis as a function of time after tethered cord release. going spinal cord untethering with curves > 40, 6 (75%) progressed, at a mean of 22 months postoperatively. Patients with Risser Grades 0 2 were 3.4 times more likely to experience scoliosis progression compared with those with Risser Grades 3 5 (hazard ratio = 3.44; p = 0.04). Although nearly all patients with Risser Grades 0 2 with curves > 40 progressed, no patients with Risser Grades 3 5 and curves < 40 progressed following spinal cord untethering (Table 3; Fig. 3). Discussion In this study of pediatric TCS-associated scoliosis, we evaluated the impact of the degree of scoliosis and skeletal maturity in children at the time of tethered cord release on the progression of scoliosis after tethered cord release. In this series of 27 patients, we observed that nearly all patients with Risser Grades 0 2 with curves > 40 experienced progression, suggesting that these patients may be most appropriate for a concurrent fusion or planned staged fusion. No children with Risser Grades 3 5 with curves < 40 showed scoliosis progression after spinal cord untethering. Skeletally immature children with curves < 40 experienced stabilization 46% of the time and progression 54% of the time after untethering. Congenital spinal abnormalities were present in 9 patients (33%), and the incidence of curve progression was not greater in this patient population. A TCS-associated syrinx was present in 4 patients (15%), and the incidence of progression in this patient cohort was 50% compared with patients without a syrinx (47%). Overall, the Risser grade and Cobb angle may help predict TCS-associated scoliosis progression and aid in selecting patients for treatment of spinal deformity. There are limited reports describing factors associated with curve progression after tethered cord release. McLone et al. 8 identified the importance of the degree of deformity at the time of untethering in their series of 30 children with myelomeningocele. In children with curves < 40, they observed that at Year 1, nearly all children remained improved or stable. However, their observed benefit diminished at the time of the last follow-up (2 7 years), as only 63% had remained stable or improved, whereas 37% experienced progression. In a series of 21 patients with myelomeningocele and scoliosis, Pierz and colleagues 11 similarly reported curve improvement or stabilization in 60% of children Fig. 2. Graph of scoliosis spinal fusion-free survival in pediatric patients with TCS-associated scoliosis as a function of time after tethered cord release. J Neurosurg: Pediatrics / Volume 4 / September 2009 Fig. 3. Graphs showing scoliosis progression-free survival (upper) and scoliosis spinal fusion-free survival (lower) in pediatric patients with TCS-associated scoliosis as a function of time after tethered cord release. Patients are grouped according to Cobb angle (< 40 or > 40 ) and Risser grade (0 2 or 3 5). 273

5 M. J. McGirt et al. with curves < 40. In our study of multiple causes of TCS with a similar duration of follow-up, we observed a greater incidence of stabilization or improvement following cord untethering in patients with curves < 40, particularly in patients with Risser Grades 3 5. Our observations also confirm prior reports demonstrating the influence of the degree of deformity and skeletal maturity on subsequent deformity progression. Although skeletal maturity has never been studied as a predictor of curve progression in patients with TCS, it has been well established in idiopathic scoliosis. Using a simplified version of the Tanner-Whitehouse III grading system, which is commonly used for classification of skeletal maturity in patients with scoliosis, Sanders et al. 17 demonstrated that skeletal maturity correlates significantly and reliably with curve behavior. The level of cord tethering has also been correlated with curve progression. In a retrospective analysis of 216 patients with TCS-associated scoliosis, Reigel et al. 14 observed that, after tethered cord release, scoliosis more frequently stabilized in patients with lumbar or sacral tethered cord. The data from the patient series of Sarwark et al. 18 support this observation. In our series, all patients had tethered spinal cords in the lumbar spine. Although this study includes the inherent limits of all retrospective analyses, all patients in this series were treated with the same practice guidelines. Following untethering, skeletally immature children underwent bracing, and the progression of scoliosis was carefully monitored using standing radiographs. All patients were followed up for at least 2 years and the mean follow-up duration was > 6 years. Nevertheless, this study is not sufficiently powered to determine the independent association of skeletal maturity, Cobb angle, and risk of scoliosis progression. Furthermore, many patients with spina bifida also have a component of congenital scoliosis unrelated to their TCS, potentially underlying the similarity in curve progression between idiopathic and TCS-associated scoliosis observed here. Conclusions In our experience with pediatric TCS-associated scoliosis, patients with Risser Grades 3 5 and Cobb angles < 40 did not experience curve progression after tethered cord release. Patients with Risser Grades 0 2 and Cobb angles > 40 were at greatest risk of curve progression after tethered cord surgery. Pediatric patients with TCSassociated scoliosis should be monitored closely for curve progression using standing radiographs after spinal cord untethering, particularly those with curves > 40 or with Risser Grades 0 2. Disclosure George I. Jallo, M.D., has received educational grants from Codman and Medtronic. References 1. 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Philadelphia: WB Saunders, 2004, Vol 3, pp Winter RB, Haven JJ, Moe JH, Lagaard SM: Diastematomyelia and congenital spine deformities. J Bone Joint Surg Am 56:27 39, 1974 Manuscript submitted December 16, Accepted April 14, Address correspondence to: Matthew J. McGirt, M.D., Department of Neurosurgery, 600 North Wolfe Street, Meyer 7-113, Bal timore, Maryland mmcgirt1@jhmi.edu. 274 J Neurosurg: Pediatrics / Volume 4 / September 2009